The present invention relates to electrical connectors for use in data communication applications where it is desirable to connect peripheral devices to a data communications bus without removing power from the bus. The present invention provides an electrical connector having variable resistance contacts such that as a first connector associated with the peripheral device and a second connector associated with the bus are mated, the resistance across the mating contacts of the two connectors varies from a relatively high resistance at the point of initial contact, to a relatively low resistance approaching 0 .OMEGA., when the connectors are fully mated.
In many computer systems, it is desirable to connect peripheral devices such as disc drives or other devices to a parallel data bus such as a Small Computer System Interface (SCSI) bus. In most older computer systems it is necessary to remove power from the bus while connecting a new peripheral device. For convenience, however, newer systems allow peripheral devices to be connected to the bus while the host system remains under power. Devices which may be connected directly to an energized bus are often referred to as "hot pluggable", and the act of connecting such a device to an active bus is known as "hot plugging". While the benefits of connecting a device directly to an energized bus without removing power are clear, hot plugging has a tendency to adversely effect data signals already present on the bus.
Generally, hot plugging is accomplished via a pair of mating connectors, each having a plurality of complimentary signal contacts. The first connector is associated with the peripheral device and mates with the second connector which is attached to the bus. Individual contacts within the connectors are attached to the various signal lines of the bus, including power, ground, and data signals. Problems arise in the first few nanoseconds as the two connectors make contact and the de-energized circuits of the hot plugging peripheral device are electrically connected to the energized circuits of the bus. As the individual signal contacts of the two connectors physically engage one another, the voltage charged on the various signal lines of the bus is pulled down as the uncharged capacitance of the peripheral device's circuits is charged. This causes a slight dip in the bus signal line voltage which can be interpreted as a data error on the signal line. Thus, data errors, or glitches, can be created when an additional peripheral device is hot plugged onto the bus.
Recently it has been determined that the problem of glitches caused by hot plugging can be ameliorated by providing a staged resistance associated with the contacts of either the peripheral connector or the bus connector. Using this approach, as the two connectors mate, the individual mating contacts initially create a high resistance path between the bus and the uncharged circuits of the hot plugging peripheral device. However, as the two connectors are moved closer to a fully mated position, the individual signal contacts move from this first high resistance stage to a second, lower resistance stage. This process of moving to progressively lower, staged resistances may be continued through any number of different resistance levels until the connectors are fully mated. In practice, 3 to 5 resistance stages have been preferred. When the contacts are fully mated, an exclusively metal to metal connection is formed such that the resistance across the connector becomes negligible.
Implementing such staged resistance contacts within a practical, commercial connector, however, as proven difficult. The foremost difficulty has been to provide a connector with variable resistance contacts in a compact package suitable for commercial use. Further, it has been difficult to produce such a connector at a reasonable cost. Thus, there exists a need for an electrical connector which presents a progressively diminishing resistance across the connector contacts as the connector transitions from an unmated to a mated position. It is desirable that such a connector should be inexpensive to produce, and capable of being conveniently packaged in a relatively compact housing.